Bit depth variable for high precision data in weighted prediction syntax and semantics

ABSTRACT

Particular embodiments provide a variable, BitDepth, that may be set at a value based on a number of bits used to represent pixels in pictures of a video. The variable may be used in syntax elements in HEVC, such as the HEVC range extension, but other coding standards may be used. By using the variable, different resolutions for the video may be accommodated during the encoding and decoding process. For example, the number of pixels in the pictures may be represented by 8 bits, 10 bits, 12 bits, or another number of bits depending on the resolution. Using the BitDepth variable in the syntax provides flexibility in the motion estimation and motion compensation process. For example, syntax elements used in the weighted prediction process may take into account different numbers of bits used to represent the pictures.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present disclosure claims priority to U.S. Provisional App. No.61/900,332, entitled “Modification of Weighted Prediction Syntax andSemantics for HEVC Range Extension”, filed Nov. 5, 2013, the contents ofwhich is incorporated herein by reference in its entirety.

BACKGROUND

The High Efficiency Video Coding (“HEVC”) coding standard (also calledH.265) is a coding standard promulgated by the ISO/IEC MPEGstandardization organizations. HEVC supports resolutions higher than“high definition,” which means pixels may be represented by a largernumber of bits than the high definition pictures. For example, 4Kresolutions may include images that are 4,000 pixels wide compared tohigh definition images that are 1920 pixels wide.

Temporal motion prediction is an effective method to increase the codingefficiency and provides high compression. HEVC uses a translationalmodel for temporal motion prediction. According to the translationalmodel, a prediction signal for a given current unit in a current pictureis generated from a corresponding reference unit in a reference picture.The coordinates of the reference unit are given by a motion vector thatdescribes the translational motion along horizontal (x) and vertical (y)directions that would be added/subtracted to/from the coordinates of thecurrent unit. A decoder needs the motion vector to decode the compressedvideo.

HEVC may use single prediction using one reference pictures orbi-prediction using two reference pictures. The pixels in referenceunits of the reference pictures are used as the prediction. In someconditions, such as when fading occurs, pixels of one of the referenceunits in bi-prediction may not yield the most accurate prediction. Tocompensate for this, HEVC may use weighted prediction when performingthe motion estimation process. Weighted prediction may weight the pixelsin one or both of the reference units used as the predictiondifferently.

SUMMARY

Embodiments of the present invention provide a variable, BitDepth, thatmay be set at a value based on a number of bits used to represent pixelsin pictures of a video. The variable may be used in syntax elements inHEVC, such as the HEVC range extension, but other coding standards maybe used. By using the variable, different resolutions for the video maybe accommodated during the encoding and decoding process. For example,the number of pixels in the pictures may be represented by 8 bits, 10bits, 12 bits, or another number of bits depending on the resolution.Using the BitDepth variable in the syntax provides flexibility in themotion estimation and motion compensation process. For example, syntaxelements used in the weighted prediction process may take into accountdifferent numbers of bits used to represent the pictures.

More particularly, a method of an embodiment of the present inventionincludes the following steps: (1) setting a first value for a variableassociated with a bit depth based on a number of bits associated withpixels of pictures in a video; (2) determining a first weighting factorfor performing weighted prediction for a current unit of a currentpicture; (3) using the first weighting factor to weight pixels of afirst reference unit of a first reference picture when performing motioncompensation for the current unit; and (4) setting a second value for aweighted prediction syntax element associated with the weighting factor,wherein the second value for the weighted prediction syntax element isbased on the first value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a simplified system for encoding and decoding videoaccording to one embodiment.

FIG. 2 depicts an example of the motion estimation and compensationprocess according to one embodiment.

FIG. 3 depicts a table of syntax elements that are used for weightedprediction according to one embodiment.

FIG. 4 depicts a simplified flowchart of a method for using the variableBitDepth in the encoding process according to one embodiment.

FIG. 5 depicts a simplified flowchart for decoding an encoded bitstreamusing the variable BitDepth according to one embodiment.

DETAILED DESCRIPTION

Described herein are techniques for performing weighted prediction. Inthe following description, for purposes of explanation, numerousexamples and specific details are set forth in order to provide athorough understanding of particular embodiments. Particular embodimentsas defined by the claims may include some or all of the features inthese examples alone or in combination with other features describedbelow, and may further include modifications and equivalents of thefeatures and concepts described herein.

Particular embodiments provide a variable, BitDepth, that may be set ata value based on a number of bits used to represent pixels in picturesof a video. The variable may be used in syntax elements in HEVC, such asthe HEVC range extension, but other coding standards may be used. Byusing the variable, different resolutions for the video may beaccommodated during the encoding and decoding process. For example, thenumber of pixels in the pictures may be represented by 8 bits, 10 bits,12 bits, or another number of bits depending on the resolution. Usingthe BitDepth variable in the syntax provides flexibility in the motionestimation and motion compensation process. For example, syntax elementsused in the weighted prediction process may take into account differentnumbers of bits used to represent the pictures.

FIG. 1 depicts a simplified system 100 for encoding and decoding videoaccording to one embodiment. System 100 includes an encoder 102 and adecoder 104. Encoder 102 and decoder 104 may use a video coding standardto encode and decode video, such as HEVC. Specifically, encoder 102 anddecoder 104 may use syntax elements from the HEVC range extension. Also,other elements of encoder 102 and decoder 104 may be appreciated.

Encoder 102 and decoder 104 perform temporal prediction through motionestimation and motion compensation. Motion estimation is a process ofdetermining a motion vector (MV) for a current unit of video. Forexample, the motion estimation process searches for a best matchprediction for a current unit of video (e.g., a prediction unit (PU))over reference pictures. The best match prediction is described by themotion vector and associated reference picture ID. Also, a referenceunit in a B picture may have up to two motion vectors that point to aprevious reference unit in a previous picture and a subsequent referenceunit in a subsequent reference picture in the picture order. Motioncompensation is then performed by subtracting a reference unit pointedto by the motion vector from the current unit of video to determine aresidual error that can be encoded. In the case of bi-prediction, thetwo motion vectors point to two reference units, which can be combinedto form a combined bi-directional reference unit. The combinedbi-directional reference unit can be subtracted from the current unit todetermine the residual error.

To perform motion estimation and compensation, encoder 102 and decoder104 include motion estimation and compensation blocks 104-1 and 104-2,respectively. In motion compensation, B and P pictures may exploit thetemporal redundancy by using weighted prediction. Weighted predictionapplies weighting factors to one or both of the reference pictures. In Ppictures, the reference unit may be weighted before being used as aprediction for the current unit. In B pictures, the reference units areweighted before combining the reference pictures into the combinedbi-directional reference unit. Conventionally, an average of thereference units from which the B picture is predicted may be used.However, using weighted prediction, a weighted average (or otherweighted calculation) of the reference units may be used to predict thecurrent unit. That is, the pixels of reference units may be weighted byweighting factors before combining. The following may be discussed withrespect to B pictures, but the discussion will also apply to P picturesexcept that the combined bi-directional reference unit is replaced byone weighted reference unit. The use of weighted prediction may beuseful when certain conditions happen in the video, such as when onescene fades into another or where there is a gradual variation inluminance, such as when fading to or from black or in cross-fades. Forexample, when fading occurs, the picture associated with the fading maynot be as accurate to use as a prediction than a picture that does notinclude the fading. Weighting the picture that does not include thefading higher may create a better prediction for the current unit. Thatis, the pixels of the reference unit that does not include the fadingeffect may have a higher correlation to the current unit. The weightingmay reduce the residual error and also reduce the bitrate.

The weighting factors may be provided for the luma and/or chromacomponents of reference units 202. Also, the weighting factors may bedifferent based on the reference list used. That is, the bi-predictionmay select a reference picture from a list0 and a list1. Referencepictures in list0 may be weighted with a weighting factor w₀ andreference pictures in list1 may be weighted with a weighting factor w₁.Also, only one of the reference pictures may be weighted. The weightingfactors may be information that adjusts the pixel values differently inthe reference units. In one embodiment, the weighting factors may bepercentages.

The weighted prediction process may use syntax elements that defineparameters that encoder 102 and decoder 104 use to perform the weightedprediction. By setting the values of these parameters, a weightedprediction manager 106-1 in encoder 102 and a weighted predictionmanager 106-2 in decoder 104 can perform the weighted predictionprocess. In a simple example, the weighting factors may weight pixels indifferent reference pictures differently. Then, weighted predictionmanagers 106-1 and 106-2 take the weighted average of the referenceunits to use as a combined bi-directional reference unit. Motionestimation and compensation blocks 104-1 and 104-2 then use thiscombined bi-directional reference unit in the motion compensationprocess for the current unit. The syntax elements will be described inmore detail below after describing the weighted prediction process inmore detail.

FIG. 2 depicts an example of the motion estimation and compensationprocess according to one embodiment. The video includes a number ofpictures 200-1-200-5. A current picture is shown at 200-3 and includes acurrent unit of video 202-1. Current unit 202-1 may be bi-predictedusing reference units from reference pictures in other pictures 200,such as a previous picture 200-1 in the picture order and a subsequentpicture 200-5 in the picture order. Picture 200-1 includes a referenceunit 202-2 and picture 200-5 includes a reference unit 202-3, both ofwhich can be used to predict current unit 202-1.

In weighted prediction, the pixels of reference units 202-2 and 202-3may be weighted differently. For example, the pixels of reference unitsmay be weighted by the weighting factors. In a simple example, theweighting factors may be percentages, such as the pixels of referenceunit 202-2 may be weighted with a weighting factor w₀ of 0.25 and thepixels of reference unit 202-3 may be weighted with a weighting factorw₁ of 0.75. These weighting factors may then be used to calculate thepixel values used as the combined bi-directional reference unit forcurrent unit 202-1.

Once the reference units are determined, motion estimation andcompensation block 104-1 can determine motion vectors that represent thelocation of reference units 202-2 and 202-3 with respect to current unit202-1. Then, motion estimation and compensation block 104-1 calculates adifference between the combined bi-directional reference unit and thecurrent unit 202-1 as a residual error.

Once determining the residual error, encoder 102 encodes the residualerror, the motion vectors, and also the weighting factors used todetermine the combined bi-directional reference unit. Encoder 102includes the encoded residual error, the motion vectors, and theweighting factors in an encoded bitstream that is sent to decoder 104.The term weighting factors is used for discussion purposes to representinformation that is encoded that allows the weighted prediction processto be performed and the weighting factors to be determined. The syntaxelements used to determine which information for the weighting factorsthat are encoded in the encoded bitstream are described in more detailbelow.

Decoder 104 receives the encoded bitstream and can reconstruct thepictures of the video. Decoder 104 may reconstruct reference units 202-2and 202-3 from the encoded bitstream prior to decoding current unit202-1. Also, decoder 104 decodes the residual error for current unit202-1, the motion vectors for current unit 202-1, and the weightingfactors. Then, in decoder 104, motion estimation and compensation block104-2 may then use the residual error to reconstruct the current unit202-1. For example, motion estimation and compensation block 104-2 mayuse the motion vectors to locate reconstructed reference units 202-2 and202-3. Then, weighted prediction manager 106-2 applies the weightingfactors to the reconstructed units 202-2 and 202-3 to form thereconstructed combined bi-directional reference unit. The reconstructedresidual error is then added to the reconstructed combinedbi-directional predicted unit to form a reconstructed current unit.

As mentioned above, syntax elements for weighted prediction may use avariable BitDepth in the weighted prediction process. The variableBitDepth may represent a number of bits used to represent a pixel in apicture. The following will describe syntax elements that use the bitdepth variable.

FIG. 3 depicts a table 300 of syntax elements that are used for weightedprediction according to one embodiment. There are syntax elements forthe luma and chroma components of the video, and also for list0 andlist1. The combined bi-directional reference unit may be determined byapplying the weighting factors in an averaging operation. In an exampleto illustrate the calculation, the weighting factor w₀ is multiplied bythe previous reference unit 202-2 (e.g., the luma and chroma componentsof the pixels) and the weighting factor w₁ is multiplied by thesubsequent reference unit 202-3 (e.g., the luma and chroma components ofthe pixels). Then, the two values are added together and divided by theadded weighting factors (e.g., normalization). The above example may notbe exactly how encoder 102 and decoder 104 perform the calculation todetermine the combined bi-directional reference unit. Various methodsmay be used, but performing a division operation may be an expensivecomputational operation. One method of deriving the weighting factors isto use bit shifting. The weighting factors can be derived with a commondenominator and the division is represented by a right shift of thecombined weighted prediction of a number of bits based on a base 2logarithm of the denominator. That is, the weighting factor, such as theluma weighting factor, may be bit shifted by the base 2 logarithm of thedenominator.

The following syntax elements encode parameter values that can be usedto perform the weighted prediction process. The syntax elements in Table300 of luma_log2_weight_denom at 302, delta_chroma_log2_weight_denom at304, delta_luma_weight_l0[i] at 306, delta_chroma_weight_l0[i][j] at308, delta_luma_weight_l1[i] at 310, and delta_chroma_weight_l1[i][j] at312 may use a BitDepth variable for the number of bits that represent apixel. This allows these syntax elements to be used for video that mayrepresent pixels with a different number of bits, such as 8, 10, 12, 14,16, etc., bits. The syntax elements can thus handle high precision data,which may represent pixels with more than 8 bits.

The syntax element luma_log2_weight_denom is the base 2 logarithm of thedenominator for all luma weighting factors. The value ofluma_log2_weight_denom shall be in the range of 0 to BitDepth_(Y),inclusive, where BitDepth_(Y) is the bit depth of the luma component ofthe reference picture. By including the range to be dependent on thevariable BitDepth_(Y), the value can represent different numbers of bitsfor the pixels. The syntax element luma_log2_weight_denom is used tocalculate the luma weighting factor (e.g., the delta luma weightingfactor of the syntax element delta_luma_weight_l0[i] anddelta_luma_weight_l1[i] described below).

The syntax element delta_chroma_log2_weight_denom is the difference ofthe base 2 logarithm of the denominator for all chroma weightingfactors. The variable ChromaLog2WeightDenom, which is the log 2denominator of the chroma weighting factor, is derived to be equal toluma_log2_weigh_denom+delta_chroma_log2_weight_denom, and the valueshall be in the range of 0 to BitDepth_(C), inclusive, where thevariable BitDepth_(C) is the bit depth of the chroma component of thereference picture. By including the range to be dependent on thevariable BitDepth_(C), the chroma weighting factor value can representdifferent numbers of bits for the pixels.

The syntax element luma_weight_l0_flag[i], when equal to 1, specifiesthat weighting factors for the luma component of list 0 prediction usingRefPicList0[i] are present. The syntax element luma_weight_l0_flag[i],when equal to 0, specifies that these weighting factors are not present.

The syntax element chroma_weight_l0_flag[i], when equal to 1, specifiesthat weighting factors for the chroma prediction values of list 0prediction using RefPicList0[i] are present. The syntax elementchroma_weight_l0_flag[i], when equal to 0, specifies that the chromaweighting factors are not present. When chroma_weight_l0_flag[i] is notpresent, it is inferred to be equal to 0.

The syntax element_delta_luma_weight_l0[i] is the difference of theweighting factor applied to the luma prediction value for list 0prediction using RefPicList0[i]. The variable LumaWeightL0[i] may be theluma weighting factor for list0 and is derived to be equal to(1<<luma_log2_weight_denom)+delta_luma_weight_l0[i]. That is, the lumaweighting factor is a right shift of the variable luma_log2_weight_denomplus the value of delta_luma_weight_l0[i]. When luma_weight_l0_flag[i]is equal to 1, the value of delta_luma_weight_l0[i] shall be in therange of −(1<<(BitDepth_(Y)−1)), (1<<(BitDepth_(Y)−1))−1, inclusive,where BitDepth_(Y) is the bit depth for the luma component of thereference picture. This sets the range of the weighting factor to bebased on the variable BitDepth_(Y). When luma_weight_l0_flag[i] is equalto 0, LumaWeightL0[i] is inferred to be equal to2^(luma_log2_weight_denom).

The syntax element luma_offset_l0[i] is the additive offset applied tothe luma prediction value for list 0 prediction using RefPicList0[i].The value of luma_offset_l0[i] shall be in the range of −128 to 127,inclusive, or −(1<<(BitDepth_(Y)−1) to (1<<(BitDepth_(Y)−1)−1,inclusive. When luma_weight_l0_flag[i] is equal to 0, luma_offset_l0[i]is inferred as equal to 0.

The syntax element delta_chroma_weight_l0[i][j] is the difference of theweighting factor applied to the chroma prediction values for list 0prediction using RefPicList0[i] with j equal to 0 for Cb and j equal to1 for Cr. The variable ChromaWeightL0[i][j] may be the chroma weightingfactor for list0 and is derived to be equal to(1<<ChromaLog2WeightDenom)−delta_chroma_weight_l0[i][j]. That is, thechroma weighting factor is a right shift of the variableChromaLog2WeightDenom plus the value of delta_chroma_weight_l0[i][j].When chroma_weight_l0_flag[i] is equal to 1, the value ofdelta_chroma_weight_l0[i][j] shall be in the range of(1<<(BitDepth_(C)−1)), (1<<(BitDepth_(C)−1))−1, inclusive, whereBitDepth_(C) is the bit depth for the chroma component of the referencepicture. This sets the range of the weighting factor to be based on thevariable BitDepth_(C). When chroma_weight_l0_flag[i] is equal to 0,ChromaWeightL0[i][j] is inferred to be equal to2^(ChromaLog2Weightdenom).

The syntax element delta_chroma_offset_l0[i][j] is the difference of theadditive offset applied to the chroma prediction values for list 0prediction using RefPicList0[i] with j equal to 0 for Cb and j equal to1 for Cr.

The variable ChromaOffsetL0[i][j] is derived as follows:

ChromaOffsetL0[i][j]=Clip3(−128, 127,(delta_chroma_offset_l0[i][j]−((128*ChromaWeightL0[i][j])>>ChromaLog2WeightDenom)+128))

The value of delta_chroma_offset_l0[i][j] shall be in the range of −512to 511, inclusive. Also, variable ChromaOffsetL0[i][j] is derived asfollows:

ChromaOffsetL0[i][j]=Clip3(−(1<<(BitDepth_(C)−1),(1<<(BitDepth_(C)−1)−1,(delta_chroma_offset_l0[i][j]−(((1<<(BitDepth_(C)1))*ChromaWeightL0[i][j])>>ChromaLog2WeightDenom)+(1<<(BitDepth_(C)−1))).

The value of delta_chroma_offset_l0[i][j] shall be in the range of−(1<<(BitDepth_(C)+1) to (1<<(BitDepth_(C)+1)−1, inclusive. Whenchroma_weight_l0_flag[i] is equal to 0, ChromaOffsetL0[i][j] is inferredto be equal to 0.

The syntax elements luma_weight_l1_flag[i], chroma_weight_l1_flag[i],delta_luma_weight_l1[i], luma_offset_l1[i],delta_chroma_weight_l1[i][j], and delta_chroma_offset_l1[i][j] have thesame semantics as luma_weight_l0_flag[i], chroma_weight_l0_flag[i],delta_luma_weight_l0[i], luma_offset_l0[i],delta_chroma_weight_l0[i][j], and delta_chroma_offset_l0[i][j],respectively, with l0, L0, list 0, and List0 replaced by l1, L1, list 1,and List1, respectively. That is, these are the same syntax elements forlist1 instead of list0.

The variable sumWeightL0Flags is derived to be equal to the sum ofluma_weight_l0_flag[i]+2*chroma_weight_l0_flag[i], for i=0 . . .num_ref_idx_l0_active_minus1. When slice type is equal to B, thevariable sumWeightL1Flags is derived to be equal to the sum ofluma_weight_l1_flag[i]+2*chroma_weight_l1_flag[i], for i=0 . . .num_ref_idx_l1_active_minus1. It is a requirement of bitstreamconformance that, when slice_type is equal to P, sumWeightL0Flags shallbe less than or equal to 24, and when slice_type is equal to B, the sumof sumWeightL0Flags and sumWeightLiFlags shall be less than or equal to24.

The above syntax elements luma offset_l0, luma_offset_l1,ChromaOffsetL0, ChromaOffsetL1 are modified when the pixels of referencepictures may include higher precision, such as when the syntax elementextended_precision_processing_flag is equal to 1.

Accordingly, by using the variable BitDepth for the luma and chromacomponents, encoder 102 may change the number of bits that is used forweighted prediction based on the number of bits that represent pixels inthe pictures of the video. In one embodiment, encoder 102 knows theBitDepth for the pictures of a video and can set the variable BitDepthto the value of the number of bits that represent the pixels ofpictures.

FIG. 4 depicts a simplified flowchart 400 of a method for using thevariable BitDepth in the encoding process according to one embodiment.At 402, encoder 102 determines a value for the variable BitDepth for theluma and chroma components. The value may be based on the precision ofthe video, such as a number of bits that represent the pixels inpictures of a video. Encoder 102 may determine the value based onanalyzing characteristics of the video. Also, the number of bits thatrepresent the pixels may be input or included in metadata associatedwith the video.

At 404, motion estimation and compensation block 104-1 determines whenweighted prediction is enabled. For example, weighted prediction flags,luma_weight_l0_flag[i] and chroma_weight_l0_flag[i], may be set toindicate that weighted prediction is enabled for the luma and chromacomponents.

At 406, weighted prediction manager 106-1 determines motion vectors forreference units 202-2 and 202-3 and weighting factors for the luma andchroma components for reference units 202-2 and 202-3 (e.g., list0 andlist1). The weighting factors may be assigned to the pictures (e.g.,list0 and list1) that are being used as reference pictures for a currentpicture.

At 408, weighted prediction manager 106-1 then calculates the combinedbi-directional reference unit to use in motion compensation based on theweighting factors and pixels of reference units 202-2 and 202-3. Asdescribed above, the weighting factors weight pixels differently inreference units 202-2 and 202-3. At 410, motion estimation andcompensation block 104-1 determines the residual error using currentunit 202-1 and the combined bi-directional reference unit.

At 412, encoder 102 calculates the values for the applicable syntaxelements used in the weighted prediction process. For example, thevalues for the syntax elements luma_log2_weight_denom,delta_chroma_log2_weight_denom, delta_luma_weight_l0[i],delta_chroma_weight_l0[i][j], delta_luma_weight_l1[i], anddelta_chroma_weight_l1[i][j] using the variable BitDepth are calculated.

At 414, encoder 102 encodes the parameters for the syntax elements forthe weighted prediction process in an encoded bitstream along with themotion vectors and residual error for current unit 202-1. For example,encoder 102 encodes the values calculated for the syntax elements shownin Table 300 in FIG. 3. At 416, encoder 102 sends the encoded bitstreamto decoder 104.

FIG. 5 depicts a simplified flowchart 500 for decoding an encodedbitstream using the variable BitDepth according to one embodiment. At502, decoder 104 receives the encoded bitstream. At 504, decoder 104then determines a current unit 202-1 in a current picture to decode. At506, decoder 104 decodes the encoded motion vectors from the encodedbitstream for current unit 202-1 and uses these motion vectors to locatethe reconstructed reference units 202-2 and 202-3. Also, at 508, decoder104 determines the residual error for current unit 202-1 from theencoded bitstream.

At 510, weighted prediction manager 106-2 may determine the values forthe syntax elements in Table 300 for weighted prediction. This may allowweighted prediction manager 106-2 to determine the weighting factors. At512, weighted prediction manager 106-2 may then apply the weightingfactors to reference units 202-2 and 202-3 to determine the combinedbi-directional reference unit. At 514, motion estimation andcompensation block 104-2 can then add the residual error for currentunit 202-1 to the combined weighted prediction unit to form areconstructed current unit.

Accordingly, particular embodiments use a variable BitDepth for syntaxelements in the weighted prediction process. For example, the syntaxelements luma_log2_weight_denom, delta_chroma_log2_weight_denom,delta_luma_weight_l0[i], delta_chroma_weight_l0[i][j],delta_luma_weight_l1[i], and delta_chroma_weight_l1[i][j] use thevariable BitDepth.

Particular embodiments may be implemented in a non-transitorycomputer-readable storage medium for use by or in connection with theinstruction execution system, apparatus, system, or machine. Thecomputer-readable storage medium contains instructions for controlling acomputer system to perform a method described by particular embodiments.The computer system may include one or more computing devices. Theinstructions, when executed by one or more computer processors, may beconfigured to perform that which is described in particular embodiments.

As used in the description herein and throughout the claims that follow,“a”, “an”, and “the” includes plural references unless the contextclearly dictates otherwise. Also, as used in the description herein andthroughout the claims that follow, the meaning of “in” includes “in” and“on” unless the context clearly dictates otherwise.

The above description illustrates various embodiments along withexamples of how aspects of particular embodiments may be implemented.The above examples and embodiments should not be deemed to be the onlyembodiments, and are presented to illustrate the flexibility andadvantages of particular embodiments as defined by the following claims.Based on the above disclosure and the following claims, otherarrangements, embodiments, implementations and equivalents may beemployed without departing from the scope hereof as defined by theclaims.

1-20. (canceled)
 21. A method for decoding a bitstream, the methodcomprising: identifying one or more weight flags signaled in thebitstream that indicates presence of weighting factors for at least oneof a luma component and/or a chroma component; determining a firstweighting factor for performing weighted prediction for a current unitof a current picture the first weighting factor for weighting pixels ofa first reference unit of a first reference picture when performingmotion compensation for the current unit; determining a second weightingfactor for weighting pixels of a second reference unit of a secondreference picture when performing motion compensation for the currentunit, wherein when weighting factors for a luma component is present:determining from a signaled delta_luma_weight_l0 syntax element adifference of the first weighting factor and the second weighting factorapplied to a luma prediction value for list 0 prediction using avariable RefPicList0[i] for a first luma component, and deriving avariable LumaWeightL0 associated with the luma component weightingfactors, wherein when the one or more weight flags indicates presence ofthe weighting factor for a luma component, LumaWeightL0 is derived to beequal to (1<<luma_log2_weight_denom)+delta_luma_weight_l0 in a range of−(1<<(BitDepthy−1)), (1<<(BitDepthy−1)−1), inclusive, whereinluma_log2_weight_denom is a base 2 logarithm of a denominator for allluma weighting factors, and BitDepthy is a bit depth for the lumacomponent of the respective reference picture; and wherein whenweighting factors for a chroma component is present: determining from adelta_chroma_weight_l0[i][j] syntax element a difference of the firstweighting factor and the second weighting factor applied to a chromaprediction value for list 0 prediction using a variable RefPicList0[i]with j equal to 0 for Cb or j equal to 1 for Cr for a second component;and deriving a variable ChromaWeightL0 associated with the chromacomponent weighting factor, wherein when the one or more weight flagsindicates presence of the weighting factor for a chroma component,ChromaWeightL0 is derived to be equal to((1<<(luma_log2_weight_denom+delta_chroma_log2_weight_denom))+delta_chroma_weight_l0, delta_chroma_weight_l0 in a range of −(1<<(BitDepthc−1)),((1<<BitDepthc−1)−1), inclusive, wherein delta_chroma_log2_weight_denomis a difference of a base 2 logarithm of a denominator for all chromaweighting factors, and BitDepthc is a bit depth for the chroma componentof the respective reference picture; wherein thedelta_chroma_weight_l0[i][j] syntax element is within the range set bythe ChromaWeightL0, and wherein the second component comprises a chromacomponent of the first reference unit or the second reference unit;wherein a determination of at least one value present in a pred weighttable is dependent on a variable ChromaArrayType; wherein saiddelta_luma_weight_l0 syntax element is included in saidpred_weight_table; wherein said luma_log_2_weight_denom is a syntaxelement in said pred weight table.
 22. One or more computer-readablememory or storage devices storing encoded data as part of a bitstream,the encoded data being organized to facilitate decoding by a videodecoder performing operations, the video decoder being implemented usingmemory and one or more processing units, the operations comprising:identifying one or more weight flags signaled in the bitstream thatindicates presence of weighting factors for at least one of a lumacomponent and/or a chroma component; determining a first weightingfactor for performing weighted prediction for a current unit of acurrent picture the first weighting factor for weighting pixels of afirst reference unit of a first reference picture when performing motioncompensation for the current unit; determining a second weighting factorfor weighting pixels of a second reference unit of a second referencepicture when performing motion compensation for the current unit,wherein when weighting factors for a luma component is present:determining from a signaled delta_luma_weight_l0 syntax element adifference of the first weighting factor and the second weighting factorapplied to a luma prediction value for list 0 prediction using avariable RefPicList0[i] for a first luma component, and deriving avariable LumaWeightL0 associated with the luma component weightingfactors, wherein when the one or more weight flags indicates presence ofthe weighting factor for a luma component, LumaWeightL0 is derived to beequal to (1<<luma_log2_weight_denom)+delta_luma_weight_l0 in a range of−(1<<(BitDepthy−1)), (1<<(BitDepthy−1)−1), inclusive, whereinluma_log2_weight_denom is a base 2 logarithm of a denominator for allluma weighting factors, and BitDepthy is a bit depth for the lumacomponent of the respective reference picture; and wherein whenweighting factors for a chroma component is present: determining from adelta_chroma_weight_l0[i][j] syntax element a difference of the firstweighting factor and the second weighting factor applied to a chromaprediction value for list 0 prediction using a variable RefPicList0[i]with j equal to 0 for Cb or j equal to 1 for Cr for a second component;and deriving a variable ChromaWeightL0 associated with the chromacomponent weighting factor, wherein when the one or more weight flagsindicates presence of the weighting factor for a chroma component,ChromaWeightL0 is derived to be equal to((1<<(luma_log2_weight_denom+delta_chroma_log2_weight_denom))+delta_chroma_weight_l0, delta_chroma_weight_l0 in a range of −(1<<(BitDepthc−1)),((1<<BitDepthc−1)−1), inclusive, wherein delta_chroma_log2_weight_denomis a difference of a base 2 logarithm of a denominator for all chromaweighting factors, and BitDepthc is a bit depth for the chroma componentof the respective reference picture; wherein thedelta_chroma_weight_l0[i][j] syntax element is within the range set bythe ChromaWeightL0, and wherein the second component comprises a chromacomponent of the first reference unit or the second reference unit;wherein a determination of at least one value present in a pred weighttable is dependent on a variable ChromaArrayType; wherein saiddelta_luma_weight_l0 syntax element is included in saidpred_weight_table; wherein said luma_log_2_weight_denom is a syntaxelement in said pred weight table.
 23. A computing device comprising: avideo encoder configured to provide a bitstream and perform operationscomprising: providing one or more weight flags signaled in the bitstreamthat indicates presence of weighting factors for at least one of a lumacomponent and/or a chroma component; wherein a first weighting factorfor performing weighted prediction for a current unit of a currentpicture the first weighting factor for weighting pixels of a firstreference unit of a first reference picture when performing motioncompensation for the current unit; wherein a second weighting factor forweighting pixels of a second reference unit of a second referencepicture when performing motion compensation for the current unit,wherein when weighting factors for a luma component is present:providing from a signaled delta_luma_weight_l0 syntax element adifference of the first weighting factor and the second weighting factorapplied to a luma prediction value for list 0 prediction using avariable RefPicList0[i] for a first luma component, and wherein avariable LumaWeightL0 associated with the luma component weightingfactors, wherein when the one or more weight flags indicates presence ofthe weighting factor for a luma component, LumaWeightL0 is derived to beequal to (1<<luma_log2_weight_denom)+delta_luma_weight_l0 in a range of−(1<<(BitDepthy−1)), (1<<(BitDepthy−1)−1), inclusive, whereinluma_log2_weight_denom is a base 2 logarithm of a denominator for allluma weighting factors, and BitDepthy is a bit depth for the lumacomponent of the respective reference picture; and wherein whenweighting factors for a chroma component is present: providing from adelta_chroma_weight_l0[i][j] syntax element a difference of the firstweighting factor and the second weighting factor applied to a chromaprediction value for list 0 prediction using a variable RefPicList0[i]with j equal to 0 for Cb or j equal to 1 for Cr for a second component;and wherein a variable ChromaWeightL0 associated with the chromacomponent weighting factor, wherein when the one or more weight flagsindicates presence of the weighting factor for a chroma component,ChromaWeightL0 is derived to be equal to((1<<(luma_log2_weight_denom+delta_chroma_log2_weight_denom))+delta_chroma_weight_l0, delta_chroma_weight_l0 in a range of −(1<<(BitDepthc−1)),((1<<BitDepthc−1)−1), inclusive, wherein delta_chroma_log2_weight_denomis a difference of a base 2 logarithm of a denominator for all chromaweighting factors, and BitDepthc is a bit depth for the chroma componentof the respective reference picture; wherein thedelta_chroma_weight_l0[i][j] syntax element is within the range set bythe ChromaWeightL0, and wherein the second component comprises a chromacomponent of the first reference unit or the second reference unit;wherein a determination of at least one value present in a pred weighttable is dependent on a variable ChromaArrayType; wherein saiddelta_luma_weight_l0 syntax element is included in saidpred_weight_table; wherein said luma_log_2_weight_denom is a syntaxelement in said pred weight table.